FIG. 6 illustrates a conventionally known nonferrous metal melting furnace for melting nonferrous metal, e.g., an aluminum alloy, for the purpose of manufacturing various types of cast products (see, for example, the Japanese Patent Publication No. 2554510). The nonferrous metal melting furnace has a configuration such that molten metal 10 is re-circulated between a heating chamber 22 and a vortex chamber 23 by a re-circulation metal pump 21, while the molten metal 10 is heated by flame 50 ejected from a burner 25 provided in the heating chamber 22, and while nonferrous metal is fed in the vortex chamber 23 through a feeding port of a feeding shoot 27. In place of the burner 25, an electric heater can be used to heat the molten metal 10.
However, when the conventional nonferrous metal melting furnace is used to melt in molten metal an undried nonferrous metal block such as an aluminum briquette made of compressed aluminum chips, the briquette can involve a steam explosion, if the briquette is completely submerged into the molten aluminum metal. It is because the briquette contains oil and moisture coming from coolant.
In order to avoid the problem mentioned above, a melting furnace may be used to directly heat and melt such briquetted chip by flame of a burner of the furnace. However, this method causes the briquetted chip to spring back to chip during a melting process, by which the sprung back chip with a thin section relative to its large surface area is directly heated and melted, resulting in an increase in oxide and a significant decrease in metal recovery rate.
In addition, FIG. 7 illustrates another method in which a relatively large drying apparatus 29 such as a rotary kiln dryer is used to pre-dry aluminum chips as they are before briquetting that are fed from a storage hopper. However, it is extremely difficult to form a briquette from these pre-dried aluminum chips, because coolant to be used as a lubricant in forming a compressed chips is also dried.
Even if a briquette can be successfully formed by such a relatively large drying apparatus 29, this adversely requires a substantially large amount of costs in installation and maintenance of the apparatus 29.
It is therefore an object of the present invention to provide a nonferrous metal melting furnace and a melting method for safely and effectively melting such an undried nonferrous metal block even if it contains oil and moisture coming from coolant.